Heat exchanger temperature change rate control

ABSTRACT

A closure bar adapted for use in a heat exchanger core includes a center void region configured to be partially filled with a phase-changing material and sealed, thereby containing the phase-changing material. The phase-changing material is configured to change phase in a forward direction as the flow of hot fluid over the closure bar begins, thereby slowing a rate of a temperature increase by absorbing a latent heat as the phase-changing material changes phase in the forward direction, and change phase in a reverse direction as the flow of hot fluid over the closure bar ceases, thereby slowing a rate of a temperature decrease by liberating the latent heat as the phase-changing material changes phase in the reverse direction. A method of producing and using the closure bar is also disclosed.

BACKGROUND

Modern aircraft engines and associated systems operate at increasinglyhigher temperatures that place greater demands on several pneumaticcomponents, including heat exchangers. Heat exchangers that operate atelevated temperatures often have short service lives and/or requireincreased maintenance as a result of high cyclic thermal stress. Thestress is caused by multiple system and component factors includingrapid flow and/or temperature transients, geometric discontinuities,stiffness discontinuities, mass discontinuities, and materials ofconstruction. For example, inlet and exit manifolds are typicallypressure vessels that are welded or bolted to a heat exchanger core ormatrix. Pressure requirements dictate the thickness of these manifolds,sometimes resulting in a relatively thick header attached to a thinnercore matrix. This mismatch in thickness and mass, while acceptable forpressure loads, conflicts with the goal of avoiding discontinuities tolimit thermal stress. Because much of the fatigue damage occurs duringstart-up and shut-down transients, it would be beneficial to slow themagnitude of these thermal transients.

In particular, hot air entering a plate-fin heat exchanger coretypically encounters closure bars of the cold circuit that it must flowaround to enter the hot circuit fin passages. Because these cold closurebars are exposed to high velocity air on three sides, the cold closurebars heat up rapidly from an initial temperature, and accordingly, cantend to expand rapidly. The stiffer surrounding structure takes longerto heat up and opposes the thermal expansion of the cold closure bars,thereby creating high material stress. Although the combined structureof the heat exchanger core eventually reaches steady state temperatures,the latent damage that occurs during the initial few seconds of theheat-up transient is cumulative, and can limits the fatigue life of theheat exchanger core. Cracking of the cold closure bars and adjacentparting sheets can impact the service life of the heat exchanger core,and/or require more frequent inspection, testing, and/or repair duringthe service life. The cold closure bars that are near the hot circuitinlet are particularly vulnerable to these effects.

Methods of controlling the rate of flow introduction to the heatexchanger core during the start-up transient by using flow-modulatingvalves and associated control systems are known in the art. Theadditional components and control systems associated with those methodscan be useful in some applications. However, it can be beneficial tohave a means of controlling the rate of the temperature increase of thecold closure bars that is integral to those cold closure bars, therebynot requiring components and control systems that are external to theheat exchanger core.

SUMMARY

A closure bar adapted for use in a heat exchanger core includes a centervoid region configured to be partially filled with a phase-changingmaterial and sealed, thereby containing the phase-changing material.

A method of producing a closure bar adapted for use in a heat exchangercore includes forming a closure bar that has a center void region,partially filling the center void region with a phase-changing material,and sealing the closure bar, thereby containing the phase-changingmaterial within the center void region.

A method of operating a heat exchanger core to reduce a rate of changeof temperature in at least one portion thereof, where the heat exchangercore includes a closure bar having a center void region partially filledwith a phase-changing material and sealed, the phase-changing materialhas at least one phase-changing point that is between an initialtemperature and a hot fluid operating temperature, and the closure baris disposed in a region of the heat exchanger core that is configured toreceive a hot fluid having a hot fluid operating temperature. The methodincludes initiating flow of the hot fluid to the heat exchanger core,slowing a rate of temperature increase by absorbing latent heat as thephase-changing material changes phase in a forward direction, ceasingthe flow of the hot fluid to the heat exchanger core, slowing a rate oftemperature decrease by liberating a latent heat as the phase-changingmaterial changes phase in a reverse direction. The phase-changingmaterial has at least one phase-changing point, melting or boiling, thatis between an initial temperature and the hot fluid operatingtemperature. The phase-changing material is configured to change phasein the forward direction as the flow of hot fluid over the closure barbegins, thereby slowing a rate of temperature increase by absorbing alatent heat as the phase-changing material changes phase in the forwarddirection, and change phase in the reverse direction as the flow of hotfluid over the closure bar ceases, thereby slowing a rate of temperaturedecrease by liberating the latent heat as the phase-changing materialchanges phase in the reverse direction. The forward-reverse directionsare boiling-condensing or melting-solidifying.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a plate-fin heat exchanger core withhollow closure bars.

FIG. 2A is an end view of the plate-fin heat exchanger core of FIG. 1showing the hot fins.

FIG. 2B is a side view of the plate-fin heat exchanger core of FIG. 1showing the cold fins.

FIG. 3A is a perspective view of a temperature rate-control closure barshown in FIG. 2B.

FIG. 3B is a cross-sectional side view of the temperature rate-controlclosure bar shown in FIG. 3A.

FIG. 3C is a cross-sectional end view of the temperature rate-controlclosure bar shown in FIG. 3A.

FIG. 4A is a graph of temperature versus time for a closure bar of theprior art.

FIG. 4B is a graph of temperature versus time for the temperaturerate-control closure bar shown in FIGS. 3A-3C.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of a plate-fin heat exchanger core withrate-control closure bars. Shown in FIG. 1 are heat exchanger core 10,bottom end sheet 12, hot closure bars 14, hot fins 16, parting sheets18, cold inlet closure bars 20, cold outlet closure bars 22, cold fins24, and top end sheet 26. Heat exchanger core 10, together with inletand outlet manifolds (not shown) on each of the hot flow and cold flowcircuits, can function as a plate-fin heat exchanger for providing acompact, low-weight, and highly-effective means of exchanging heat froma hot fluid to a cold fluid. Because heat exchanger core 10 transfersheat from one fluid to another while maintaining a fluid separationbetween the two, heat will generally flow from the hot fluid to the coldfluid across the various components in heat exchanger core 10, describedhereafter. Therefore, as used in this disclosure, “hot” will be used todescribe the first fluid circuit and “cold” will be used to describe thesecond fluid circuit. The terms “hot” and “cold” are relative one to theother. As used in different embodiments, heat exchanger core 10 canencounter temperatures ranging from near absolute zero (for example, incryogenic distillation) to 1,300 deg. F (704 deg. C) or more (forexample, in gas turbine engine systems and related components).Moreover, “hot” and “cold” are used in this disclosure as descriptiveterms to refer to the various components that are associated with therespective first and second fluid circuits in the heat exchanger core,without implying that particular temperatures or a temperaturerelationship exists for those components during the manufacturingprocess of heat exchanger core 10.

Alternating hot and cold layers are sandwiched between bottom end sheet12 and top end sheet 26. Hot fins 16 channel hot flow, with boundariesdefined by hot closure bars 14 on either side of each hot layer, andparting sheets 18 on the top and bottom of each layer (with theexception of the bottom layer which is bounded on the bottom by bottomend sheet 12, and the top layer which is bounded on the top by top endsheet 26). Similarly, cold fins 24 channel cold flow, with boundariesdefined by cold inlet closure bars 20 and cold outlet closure bars 22 oneither side of each cold layer, and parting sheets 18 on the top andbottom of each layer. It is to be appreciated that cold inlet closurebars 20 are so-named because they are in the vicinity of the hot flowinlet to heat exchanger core 10. Similarly, cold outlet closure bars 22are so-named because they are in the vicinity of the hot flow outletfrom heat exchanger core 10.

In the illustrated embodiment, hot fins 16 and cold fins 24 arecorrugated. In other embodiments, hot fins 16 and/or cold fins 24 canhave any configuration, with non-limiting examples being rectangular,triangular, perforated, serrated, ruffled, and herringbone. In theillustrated exemplary embodiment, five hot layers and four cold layersare used. In other embodiments, there can be practically any number ofhot layers and cold layers, and the number of hot layers can bedifferent from the number of cold layers. For example, in a particularembodiment, there can be more than 100 layers (i.e., hot layers and coldlayers). In referring to heat exchanger core 10 shown in FIG. 1, heightwill refer to a dimension in the vertical direction as shown in FIG. 1,and width will refer to a dimension in an orthogonal direction along anappropriate axis that is defined by either hot flow or cold flow. Inreferring to the width of a particular hot or cold layer, reference canalso be made to length, for example, when describing the length of theassociated closure bars. Of course, after assembly into a heat exchanger(not shown), heat exchanger core 10 can have any physical orientationwithout regard to the labels of height, width, and/or length as are usedherein.

As noted earlier, heat exchanger core 10 can operate at elevatedtemperatures such as those in modern aircraft engines, where a typicalapplication can be to provide cooling of super-heated gas. When heatexchanger core 10 is not being used to exchange heat (i.e., theassociated heat exchanger is idle), heat exchanger core 10 componentsare at an initial temperature (T_(Init)) which can often be much coolerthan the operating temperature. The initial temperature (T_(Init)) canalso be referred to as a local ambient temperature, or as an idletemperature that is representative of the temperature of heat exchangercore 10 when not in operation. Accordingly, the initial temperature(T_(Init)) can vary depending on the local environmental conditions.During a system start-up, when heat exchanger core 10 (and accordingly,the associated heat exchanger) is put into operation, cold flow isinitiated through the cold layers and hot flow is initiated through thehot layers. Accordingly, cold inlet closure bars 20 can be subjected toa rapid heat-up as the hot fluid having hot fluid temperature (T_(H))flows over (i.e., flows past, flows around) cold inlet closure bars 20into hot fins 16. The advantage of the present disclosure can bedescribed by contrasting the start-up transient of heat exchanger core10 to that of a plate-fin heat exchanger of the prior art (not shown),in which a hot flow is directed at the cold inlet closure bars, therebyquickly raising their temperature from ambient temperature to asteady-state operating temperature. This heat-up transient can result intransient stress-loading in heat exchanger core 10 particularly in andnear cold inlet closure bars 20, which can affect the service lifeand/or the maintenance requirements. As will be described in regard tothe figures that follow, heat exchanger core 10 of the presentdisclosure provides temperature increase rate control during thestart-up transient which can lower the cyclic stress loading on heatexchanger core 10, thereby reducing maintenance requirements and/orextending the service life.

FIG. 2A is an end view of the plate-fin heat exchanger core of FIG. 1 inwhich hot fins 16 are visible. FIG. 2B is a side view of the plate-finheat exchanger core of FIG. 1 in which cold fins 24 are visible. Shownin FIGS. 2A-2B are bottom end sheet 12, hot closure bars 14, hot fins16, parting sheets 18, cold inlet closure bars 20, cold outlet closurebars 22, cold fins 24, and top end sheet 26, having descriptionssubstantially similar to those provided above in regard to FIG. 1. Alsoshown in FIG. 1 are rate-control cores 30, shown in phantom, which arelocated within cold inlet closure bars 20. As described above in regardto FIG. 1, cold inlet closure bars 20 (i.e., near the hot fluid inlet)are subject to an extreme temperature transient within heat exchangercore 10. Therefore, rate-control cores 30 are used to mitigate thetemperature transient that cold inlet closure bars 20 experience,prolonging the heat-up transient and thereby reducing the cyclic stressloading. As used in this disclosure, rate-control core 30 can also bereferred to as a temperature rate-control core.

In the illustrated embodiment, rate-control cores 30 are located withincold inlet closure bars 20, which are exposed to the hot fluidtemperature (T_(H)) during the heat-up transient. In some embodiments,some or all cold outlet closure bars 22 can also include a rate-controlcore 30. In these and/or other embodiments, some (i.e., at least one)cold inlet closure bars 20 can include rate-control cores 30. Cold inletclosure bars 20, which include rate-control cores 30, can also bereferred to as temperature rate-control closure bars, or simply, asrate-control closure bars. Accordingly, as used in the presentdisclosure, cold inlet closure bars 20 and temperature rate-controlclosure bars 20 can be used interchangeably. In the illustratedembodiment, heat exchanger core 10 and its components (includingtemperature rate-control closure bars 20) can be assembled andmetallurgically joined using one of several exemplary processesincluding brazing and welding (e.g., electron beam welding). In someembodiments, heat exchanger core 10 and its components can bemanufactured by additive manufacturing, hybrid additive subtractivemanufacturing, subtractive manufacturing, and/or casting, for example.Embodiments of features described herein can leverage any additive orpartial-additive manufacturing method is within the scope of the presentdisclosure.

FIG. 3A is a perspective view of temperature rate-control closure bar 20shown in FIG. 2B. FIG. 3B is a cross-sectional side view of temperaturerate-control closure bar 20. FIG. 3C is a cross-sectional end view oftemperature rate-control closure bar 20. Shown in FIGS. 3A-3C aretemperature rate-control closure bar 20, rate-control core 30,upper/lower wall 32, sidewall 34, end plug 36, weld 38, chamfer 40,phase-changing material 50, and void space 54. Also labeled in FIGS.3B-3C are bar length L, bar height H, bar width W, core diameter D,sidewall thickness A, and upper/lower wall thickness B. In theillustrated embodiment, temperature rate-control closure bar 20 is firstfabricated having void space 54 on the interior, and then later filledor partially-filled with phase-changing material 50 by affixing end plug36 at each end. Temperature rate-control closure bar 20 is made of metalor a metal alloy, with non-limiting examples of metallic materialsincluding nickel, aluminum, titanium, copper, iron, cobalt, and/or allalloys that include these various metals. In an exemplary embodiment,temperature rate-control closure bar 20 can be a corrosion-resistantsteel (i.e., CRES, stainless steel). Temperature rate-control closurebar 20 can be made by extrusion. In some embodiments, temperaturerate-control closure bar 20 can be formed by additive manufacturing,hybrid additive subtractive manufacturing, subtractive manufacturing,casting, and/or forging, for example. In other embodiments that utilizeadditive manufacturing processes, temperature rate-control closure bar20 can be made from any of the previously listed metals and/or theiralloys. In some of these other embodiments, various alloys of INCONEL™can be used, with Inconel 625 and Inconel 718 being two exemplary alloyformulations. In other embodiments, HAYNES™ 282 can be used. In theillustrated embodiment, chamfer 40 is located on each of theoutward-facing corners (i.e., the corners that are incident to the hotflow entering heat exchanger core 10). Chamfers 40 can help reducestress in temperature rate-control closure bar 20. In some embodiments,chamfers 40 can also assist in the aerodynamic/hydrodynamic propertiesof heat exchanger core 10 (e.g., flow channeling, flow smoothing). Inother embodiments, one or both chamfers 40 can be omitted fromtemperature rate-control closure bars 20.

Referring to FIGS. 3B-3C, temperature rate-control closure bar 20 hasbar length L, bar height H, and bar width W. In the illustratedembodiment, bar length L is about 12 cm (5 inches), bar height H isabout 4 mm (0.16 in), bar width W is about 4.5 mm (0.18 inch), corediameter D is about 2 mm (0.08 in), sidewall thickness A is about 1.25mm (0.05 inch), and upper/lower wall thickness B is about 1 mm (0.04inch). In some embodiments, bar length L can range from about 5 cm (2inches) to about 1.8 m (6 feet). In other embodiments, bar height H canrange from about 0.64 mm (0.025 inch) to about 25 mm (1 inch). It is tobe appreciated that in an exemplary embodiment, the dimensions of barheight H, bar width W, core diameter D, sidewall thickness A, andupper/lower wall thickness B can roughly scale with each other, therebymaintaining a cross-sectional aspect that is roughly similar to thatdepicted in FIG. 3C, however these dimensions can vary widely whilekeeping within the scope of the present embodiment. In the illustratedembodiment, the cross-sectional shape of rate-control core 30 iscircular (i.e., having core diameter D). In some embodiments, thecross-sectional shape of rate-control core 30 can be elliptical, oval,oblong, or polygonal. As used in the present disclosure, rate-controlcore 30 refers to the hollow internal region of temperature rate-controlclosure bar 20 and any included fill material (i.e., phase-changingmaterial 50 in solid, liquid, and/or gaseous phase, and any remainingvoid space). The hollow internal region can also be referred to as acenter void region.

Referring again to FIGS. 3B-3C, temperature rate-control closure bar 20contains phase-changing material 50 which fills a portion ofrate-control core 30. In the illustrated embodiment, phase-changingmaterial 50 is a liquid at ambient temperature and void space 54occupies the remainder of the volume of rate-control core 30. Void space54 can also be referred to as a residual void volume. In the illustratedembodiment, void space 54 is filled with air. In some embodiments, voidspace 54 can be filled with an inert gas, with helium, nitrogen, andargon being non-limiting examples. In other embodiments, void space 54can be evacuated, thereby containing a vacuum. In some of these otherembodiments, a partial vacuum (i.e., rarefied air and/or gas) can exist.End plug 36 hermetically seals each end of temperature rate-controlclosure bar 20, thereby containing phase-changing material 50. End plug36 can have a thickness (not labeled) that is on the order of magnitudeof sidewall thickness A. In the illustrated embodiment, welds 38metallurgically join end plugs 36 to temperature rate-control closurebar 20. In some embodiments, the metallurgically joining can be bybrazing. In other embodiments, end plugs 36 can be joined to temperaturerate-control closure bar 20 by interference fit or by the use of athreaded fastener (e.g., cap screw). In the illustrated embodiment, wallcoating 48 coats the interior of temperature rate-control closure bar 20(i.e., the interior surfaces of upper/lower walls 32, sidewalls 34, andend plugs 36). Wall coating 48 is a material that reduces or preventsthe reaction of phase-changing material 50 with the material oftemperature rate-control closure bars 20. In an exemplary embodiment,wall coating 48 is high-temperature paint. In other embodiments, wallcoating can be a polymer coating, ceramic coating, or a plating. In someof these other embodiments, wall coating can be metallic plating. Anexemplary metallic plating is electroless nickel. In some embodiments,wall coating 48 can be omitted from some or all surfaces of rate-controlcore 30 (i.e., interior surfaces of temperature rate-control closure bar20).

In the illustrated embodiment, phase-changing material 50 occupiesapproximately 30% of the volume of rate-control core 30 at ambienttemperature (T_(Amb)). This can also be referred to as a fill volumeratio. In some embodiments, phase-changing material 50 can occupybetween 25-35% of the volume of rate-control core 30 at ambienttemperature (T_(Amb)). In other embodiments, phase-changing material 50can occupy between 20-95% of the volume of rate-control core 30 atambient temperature (T_(Amb)). It is to be appreciated that asphase-changing material 50 boils, void space 54 begins to fill with avapor of phase-changing material 50. As used in this disclosure, ambienttemperature (T_(Amb)) is taken to be 20 deg. C (68 deg. F), unlessotherwise specified.

FIG. 4A is a graph of temperature versus time for a closure bar of theprior art, obtained from mathematical modeling. Shown in FIG. 4A are hotfluid temperature plot 60, hot fluid heat-up region 62, cold closure barbulk temperature plot 64, cold closure bar heat-up region 66, and coldclosure bar steady state point 68. The units of temperature are degreesCelsius (C) with initial temperature (T_(Init)) indicated at thehorizontal axis, however specific temperature values are not necessaryto the description. The units of time are seconds (s) with zerobeginning at the vertical axis, however specific time values are notnecessary to the description. As described above in regard to FIG. 1,initial temperature (T_(Init)) is the temperature of heat exchanger core10 in an idle condition, which can be influenced by the localenvironmental condition. In the illustrated embodiment, initialtemperature (T_(Init)) is about 50 deg. F (10 deg. C), which can beexemplary of the local environmental condition for an aircraft that isidle on the ground. At time zero (i.e., t=0), hot fluid is directed atthe heat exchanger core of the prior art and the hot fluid temperaturebegins to rise during hot fluid heat-up region 62. Eventually, hot fluidtemperature achieves the steady-state value of hot fluid temperature(T_(H)). As the hot fluid flows past the cold inlet closure bars of theprior art, cold closure bar bulk temperature begins to rise in responseto the incoming hot fluid flow, during cold closure bar heat-up region66. Eventually, cold closure bar bulk temperature achieves cold closurebar bulk steady state temperature (T_(SS)) at cold closure bar steadystate point 68 corresponding to the time to steady state (t₁).Accordingly, the stress loading on the cold inlet closure bars is aresult of the temperature excursion from initial temperature (T_(Init))to cold closure bar bulk steady state temperature (T_(SS)) over time tosteady state (t₁). It is to be appreciated that during steady state,cold closure bar bulk steady state temperature (T_(SS)) is less than hotfluid temperature (T_(H)) as a result of the heat flux across the coldinlet closure bar.

FIG. 4B is a graph of temperature versus time for temperaturerate-control closure bar 20, obtained from mathematical modeling. Theadvantages of temperature rate-control closure bar 20 of the presentdisclosure are described in contrast to FIG. 4A showing the closure barof the prior art, while using a common time scale. Shown in FIG. 4B arehot fluid temperature plot 70, hot fluid heat-up region 72, cold closurebar bulk temperature plot 74, cold closure bar first heat-up region 76,phase change begin point 78, phase change region 80, phase change endpoint 82, cold closure bar second heat-up region 84, and cold closurebar steady state point 86. As noted above in regard to FIG. 4A, theunits of temperature are degrees Celsius (C), with initial temperature(T_(Init)) indicated at the horizontal axis, however specifictemperature values are not necessary to the description. Similarly, theunits of time are seconds (s), with zero beginning at the vertical axis,however specific time values are not necessary to the description. Asdescribed above in regard to FIG. 1, initial temperature (T_(Init)) isthe temperature of heat exchanger core 10 in an idle condition. In theillustrated embodiment, initial temperature (T_(Init)) is about 50 deg.F (10 deg. C). Accordingly, At time zero (i.e., t=0), hot fluid isdirected at heat exchanger core 10 and the entering hot fluidtemperature begins to rise during hot fluid heat-up region 72.Eventually, hot fluid temperature achieves the steady-state value of hotfluid temperature (T_(H)). As the hot fluid flows past cold inletclosure bars 20, cold closure bar bulk temperature begins to rise inresponse to the incoming hot fluid flow, during cold closure bar firstheat-up region 76. Eventually, phase-changing material 50 begins to boilat phase change begin point 78. Phase-changing material 50 absorbs heatenergy through the latent heat of vaporization (LHV), while maintainingessentially a steady temperature during phase change region 80.Eventually, phase-changing material 50 has been converted into vapor(i.e., all available LHV has been absorbed) at phase change end point82, and cold closure bar bulk temperature begins to rise again.Eventually, cold closure bar bulk temperature achieves cold closure barbulk steady state temperature (T_(SS)) at cold closure bar steady statepoint 86, corresponding to phase-changing time to steady state (t₂). Ascan be seen from FIGS. 4A-4B, the phase-changing time to steady state(t₂) is greater than the time to steady state (t₁) for a heat exchangercore of the prior art, thereby prolonging the heat-up of cold inletclosure bars 20. Accordingly, the stress loading on temperaturerate-control closure bars 20 is less than that of the prior art becausethe temperature excursion from initial temperature (T_(Init)) to coldclosure bar bulk steady state temperature (T_(SS)) occurs over a muchlonger phase-changing time to steady state (t₂). Stated alternatively,the aggregate heat-up rate (i.e., the change in temperature divided bythe change in time) is lower. It is to be appreciated that during steadystate, the cold closure bar bulk steady state temperature (T_(SS)) isless than the hot fluid temperature (T_(H)) as a result of the heat fluxacross temperature rate-control closure bars 20.

In the illustrated embodiment, phase-changing time to steady state (t₂)is about 2.5 times the value of time to steady state (t₁) in the priorart. The ratio of t₂ to t₁ can be referred to as the heat-upprolongation factor. In some embodiments, the heat-up prolongationfactor can range from about 1.5-10. In other embodiments, the heat-upprolongation factor can be greater than 10. It is to be appreciated thatseveral factors can affect the heat-up prolongation factor in aparticular embodiment, with non-limiting examples including the hotfluid temperature (T_(H)), the physical size of temperature rate-controlclosure bars 20, the volume of rate control core 30, the specific heatcapacity and thermal conductivity of temperature rate-control closurebars 20, the material used for phase-changing material 50, and the fillvolume percentage.

As described above in regard to FIG. 4B, phase-changing material 50 isselected to have a boiling point that occurs during the temperaturetransient when hot flow is initiated into heat exchanger core 10 (i.e.,during the heat-up phase). Accordingly, when phase-changing material 50reaches the boiling point, its temperature will remain relativelyconstant during boiling, as heat is absorbed by the latent heat ofvaporization (LHV). In the illustrated embodiment, phase-changingmaterial 50 is water. In some embodiments, phase-changing material 50can be any compound that has a boiling point that occurs during thetemperature heat-up transient of heat exchanger core 10, withnon-limiting examples including acetone, methanol, and titaniumtetrachloride.

In some embodiments, phase-changing material 50 can be a solid atambient temperature, with the phase-change temperature representing amelting point. Accordingly, phase-changing material 50 is selected tohave a melting temperature that occurs during the temperature transientwhen hot flow is initiated into heat exchanger core 10 (i.e., during theheat-up phase). In these embodiments, phase-changing material 50 absorbsheat energy through the latent heat of fusion (LHF), while maintainingessentially a steady temperature during phase change region 80, withnon-limiting examples including includes sodium, potassium, cesium,lithium, and their salts. In these embodiments, phase-changing material50 can be inserted within temperature rate-control closure bars 20during the manufacturing process in any form including a solid rod,pellets, and/or a powder. Moreover, in these embodiments, the fillvolume ratio can be any value up to 100%, because it can be unnecessaryto accommodate a vapor phase of phase-changing material 50. In anexemplary embodiment, the fill volume ratio can be about 90%, therebyallowing a small void space 54 to accommodate the thermal expansion ofphase-changing material 50 within temperature rate-control closure bar20. In other embodiments, phase-changing material 50 can undergo bothmelting and boiling during the heat-up of temperature rate-controlclosure bars 20, thereby resulting in two regions of steady temperature(i.e., two temperature plateaus) in cold closure bar bulk temperatureplot 74.

It is to be appreciated that for most materials, phase-changing is areversible process in which the heat energy (i.e., LHV) that is absorbedduring vaporization (i.e., changing phase from liquid to gaseous) islater liberated during condensation (i.e., changing phase from gaseousto liquid). Similarly, the heat energy (i.e., LHF) that is absorbedduring melting (i.e., changing phase from solid to liquid) is laterliberated during freezing (i.e., changing phase from liquid to solid).Accordingly, the present disclosure also provides temperature decreaserate control by lengthening the period of time it takes for temperaturerate-control closure bars 20 to cool down from an operating temperatureto a final temperature. Phase-changing material 50 can therefore said tohave a forward and a reverse phase-changing direction. In a particularembodiment, the forward-reverse phase-changing direction pair can beboiling-condensing. In another particular embodiment, theforward-reverse phase-changing direction pair can bemelting-solidifying. In some embodiments, phase-changing material 50 canhave two phase-changing temperatures (i.e., melting and boiling) thatoccur between the initial temperature (T_(Init)) and the hot fluidtemperature (T_(H)).

Moreover, it is to be appreciated that initial temperature (T_(Init))can vary widely under various embodiments. In an exemplary embodimentwhere heat exchanger core 10 is on an aircraft that is parked on theground, initial temperature (T_(Init)) can range from about −70 deg F to140 deg. F (−57 deg C. to 60 deg C). In another embodiment, for example,where heat exchanger core 10 is exposed to cold circuit fan air prior toinitiating hot air flow by the opening of a shut-off valve, initialtemperature (T_(Init)) can be about 300 deg. F (149 deg. C). In yetother embodiments, initial temperature (T_(Init)) can be an elevatedtemperature (e.g., an operating temperature), whereby temperaturerate-control closure bars 20 provide cool-down rate control.Accordingly, initial temperature (T_(Init)) ranging from near absolutezero (for example, in cryogenic distillation) to 1,300 deg. F (704 deg.C) or more are within the scope of the present disclosure. Therefore,the selection of phase-changing material 50 can be influenced by theexpected range of temperatures that can be encountered in any particularembodiment.

In the embodiment shown in FIGS. 2A-2B and 3A-3C, phase-changingmaterial 50 was used in cold inlet closure bar 20 of heat exchanger core10, depicted as being a plate-fin heat exchanger core. All bars havingrate-control core 30 that includes phase-changing material 50 for use ina heat exchanger core are within the scope of the present disclosure,whereby their use can include slowing the rate of temperature increaseby absorbing latent heat as the phase-changing material changes phase inthe forward direction (e.g., melting or boiling), and/or slowing therate of temperature decrease by liberating the latent heat as thephase-changing material changes phase in the reverse direction (e.g.,solidifying or condensing).

Discussion of Possible Embodiments

A closure bar adapted for use in a heat exchanger core, the closure barcomprising a center void region configured to be partially filled with aphase-changing material and sealed, thereby containing thephase-changing material.

The closure bar of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the foregoing closure bar, wherein: the centervoid region defines a center void region volume; the center void regionis filled with the phase-changing material; and the phase-changingmaterial fills between 20-95% of the center void region volume at anambient temperature, thereby defining a residual void volume.

A further embodiment of the foregoing closure bar, wherein the residualvoid volume contains a vacuum.

A further embodiment of the foregoing closure bar, wherein the residualvoid volume is filled with a gas that includes argon, helium, nitrogen,air, or mixtures thereof.

A further embodiment of the foregoing closure bar, wherein: the closurebar is configured to be subjected to a flow of a hot fluid having a hotfluid operating temperature; the phase-changing material has a boilingpoint that is between an initial temperature and the hot fluid operatingtemperature; and the phase-changing material is configured to: boil asthe flow of hot fluid over the closure bar begins, thereby slowing arate of temperature increase by absorbing a latent heat of vaporizationas the phase-changing material boils; and condense as the flow of hotfluid over the closure bar ceases, thereby slowing a rate of temperaturedecrease by liberating the latent heat of vaporization as thephase-changing material condenses.

A further embodiment of the foregoing closure bar, wherein: the closurebar is configured to be subjected to a flow of a hot fluid having a hotfluid operating temperature; the phase-changing material has a meltingpoint that is between an initial temperature and the hot fluid operatingtemperature; and the phase-changing material is configured to: melt asthe flow of hot fluid over the closure bar begins, thereby slowing arate of temperature increase by absorbing a latent heat of fusion as thephase-changing material melts; and solidify as the flow of hot fluidover the closure bar ceases, thereby slowing a rate of temperaturedecrease by liberating the latent heat of fusion as the phase-changingmaterial solidifies.

A further embodiment of the foregoing closure bar, wherein thephase-changing material is selected from the group consisting of:sodium, potassium, cesium, lithium, and salts thereof.

A further embodiment of the foregoing closure bar, wherein: thephase-changing material additionally has a boiling point that is betweenthe melting point and the hot fluid operating temperature; and thephase-changing material is configured to: boil as the flow of hot fluidover the closure bar continues, thereby further slowing the rate oftemperature increase by absorbing a latent heat of vaporization as thephase-changing material boils; and condense as the flow of hot fluidover the closure bar ceases, thereby further slowing the rate oftemperature decrease by liberating the latent heat of vaporization asthe phase-changing material condenses.

A further embodiment of the foregoing closure bar, wherein thephase-changing material is selected from the group consisting of water,acetone, methanol, titanium tetrachloride, and mixtures thereof.

A further embodiment of the foregoing closure bar, further comprisingone or more materials selected from the group consisting of nickel,aluminum, titanium, copper, iron, cobalt, and alloys thereof.

A further embodiment of the foregoing closure bar, wherein each centervoid region is configured to be sealed by a method selected from thegroup consisting of: brazing, welding, sealing with aninterference-fitted plug, and sealing with a threaded fitting.

A further embodiment of the foregoing closure bar, wherein: the centervoid region defines an interior surface; and the interior surface iscoated with a material that is configured to prevent the phase-changingmaterial from reacting with the first cold closure bars.

A further embodiment of the foregoing closure bar, further comprising aheat exchanger core comprising: a bottom end sheet; a plurality ofalternately stacked individual hot and cold layers, the cold layersdefining a hot layer inlet region and a hot layer outlet region; and atop end sheet; wherein: each individual hot layer includes: a hot finelement forming a plurality of parallel open-ended hot channels adaptedto pass a fluid therethrough; a parting sheet separating each individualhot layer from the adjacent individual cold layer; and two hot closurebars positioned on opposite sides of the fin element, parallel to theopen-ended hot channels and extending the length of the open-ended hotchannels; each individual cold layer includes: a cold fin elementforming a plurality of parallel open-ended cold channels adapted to passa fluid therethrough; a parting sheet separating each individual coldlayer from the adjacent individual hot layer; a first cold closure bar,positioned on a first side of the cold fin element proximate the hotlayer inlet region, parallel to the open-ended cold channels andextending the length of the open-ended cold channels; and a second coldclosure bar, positioned on a second side of the cold fin elementproximate to the hot layer outlet region and opposite the first coldclosure bar, parallel to the open-ended cold channels and extending thelength of the open-ended cold channels; wherein the second cold closurebar is the foregoing closure bar.

The heat exchanger of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the foregoing heat exchanger, wherein: eachindividual hot layer comprises two hot closure bars, each defining a hotclosure height between 0.64-25 mm (0.025-1 inch); and each individualcold layer comprises two cold closure bars, each defining a cold closureheight between 0.64-25 mm (0.025-1 inch).

A further embodiment of the foregoing heat exchanger, wherein the heatexchanger core is manufactured by one or more processes selected fromthe group consisting of: additive manufacturing, hybrid additivemanufacturing, subtractive manufacturing, and hybrid additivesubtractive manufacturing.

A method of producing a closure bar adapted for use in a heat exchangercore, the method comprising: forming a closure bar, the closure bardefining a center void region; partially filling the center void regionwith a phase-changing material; and sealing the closure bar, therebycontaining the phase-changing material within the center void region.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the foregoing method, wherein: the center voidregion is configured to be sealed by a method selected from the groupconsisting of: brazing, welding, sealing with an interference-fittedplug, and sealing with a threaded fitting; and the closure bar comprisesone or more materials selected from the group consisting of nickel,aluminum, titanium, copper, iron, cobalt, and alloys thereof.

A further embodiment of the foregoing method, wherein: the closure baris configured to be subjected to a flow of a hot fluid having a hotfluid operating temperature; the phase-changing material has at leastone phase-changing point that is between an initial temperature and thehot fluid operating temperature; wherein the at least one phase-changingpoint is selected from the group consisting of: melting and boiling; thephase-changing material is configured to: change phase in a forwarddirection as the flow of hot fluid over the closure bar begins, therebyslowing a rate of temperature increase by absorbing a latent heat as thephase-changing material changes phase in the forward direction; andchange phase in a reverse direction as the flow of hot fluid over theclosure bar ceases, thereby slowing a rate of temperature decrease byliberating the latent heat as the phase-changing material changes phasein the reverse direction; wherein the forward-reverse directions areselected from the group consisting of: boiling-condensing andmelting-solidifying.

A method of operating a heat exchanger core to reduce a rate of changeof temperature in at least one portion thereof, wherein the heatexchanger core includes a closure bar having a center void regionpartially filled with a phase-changing material and sealed, thephase-changing material has at least one phase-changing point that isbetween an initial temperature and a hot fluid operating temperature,and the closure bar is disposed in a region of the heat exchanger corethat is configured to receive a hot fluid having a hot fluid operatingtemperature, the method comprising: initiating a flow of the hot fluidto the heat exchanger core; slowing a rate of temperature increase byabsorbing a latent heat as the phase-changing material changes phase ina forward direction; ceasing the flow of the hot fluid to the heatexchanger core; and slowing a rate of temperature decrease by liberatinga latent heat as the phase-changing material changes phase in a reversedirection; wherein: the phase-changing material has at least onephase-changing point that is between an initial temperature and the hotfluid operating temperature; wherein the at least one phase-changingpoint is selected from the group consisting of: melting and boiling; thephase-changing material is configured to: change phase in the forwarddirection as the flow of hot fluid over the closure bar begins, therebyslowing a rate of temperature increase by absorbing a latent heat as thephase-changing material changes phase in the forward direction; andchange phase in the reverse direction as the flow of hot fluid over theclosure bar ceases, thereby slowing a rate of temperature decrease byliberating the latent heat as the phase-changing material changes phasein the reverse direction; and the forward-reverse directions areselected from the group consisting of: boiling-condensing andmelting-solidifying.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the foregoing method, wherein: the center voidregion is configured to be sealed by a method selected from the groupconsisting of: brazing, welding, sealing with an interference-fittedplug, and sealing with a threaded fitting; and the closure bar comprisesone or more materials selected from the group consisting of nickel,aluminum, titanium, copper, iron, cobalt, and alloys thereof.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A closure bar adapted for use in a heat exchanger core, the closurebar comprising a center void region configured to be partially filledwith a phase-changing material and sealed, thereby containing thephase-changing material.
 2. The closure bar of claim 1, wherein: thecenter void region defines a center void region volume; the center voidregion is filled with the phase-changing material; and thephase-changing material fills between 20-95% of the center void regionvolume at an ambient temperature, thereby defining a residual voidvolume.
 3. The closure bar of claim 2, wherein the residual void volumecontains a vacuum.
 4. The closure bar of claim 2, wherein the residualvoid volume is filled with a gas that includes argon, helium, nitrogen,air, or mixtures thereof.
 5. The closure bar of claim 2, wherein: theclosure bar is configured to be subjected to a flow of a hot fluidhaving a hot fluid operating temperature; the phase-changing materialhas a boiling point that is between an initial temperature and the hotfluid operating temperature; and the phase-changing material isconfigured to: boil as the flow of hot fluid over the closure barbegins, thereby slowing a rate of temperature increase by absorbing alatent heat of vaporization as the phase-changing material boils; andcondense as the flow of hot fluid over the closure bar ceases, therebyslowing a rate of temperature decrease by liberating the latent heat ofvaporization as the phase-changing material condenses.
 6. The closurebar of claim 2, wherein: the closure bar is configured to be subjectedto a flow of a hot fluid having a hot fluid operating temperature; thephase-changing material has a melting point that is between an initialtemperature and the hot fluid operating temperature; and thephase-changing material is configured to: melt as the flow of hot fluidover the closure bar begins, thereby slowing a rate of temperatureincrease by absorbing a latent heat of fusion as the phase-changingmaterial melts; and solidify as the flow of hot fluid over the closurebar ceases, thereby slowing a rate of temperature decrease by liberatingthe latent heat of fusion as the phase-changing material solidifies. 7.The heat exchanger core of claim 6, wherein the phase-changing materialis selected from the group consisting of: sodium, potassium, cesium,lithium, and salts thereof.
 8. The heat exchanger core of claim 6,wherein: the phase-changing material additionally has a boiling pointthat is between the melting point and the hot fluid operatingtemperature; and the phase-changing material is configured to: boil asthe flow of hot fluid over the closure bar continues, thereby furtherslowing the rate of temperature increase by absorbing a latent heat ofvaporization as the phase-changing material boils; and condense as theflow of hot fluid over the closure bar ceases, thereby further slowingthe rate of temperature decrease by liberating the latent heat ofvaporization as the phase-changing material condenses.
 9. The closurebar of claim 1, wherein the phase-changing material is selected from thegroup consisting of water, acetone, methanol, titanium tetrachloride,and mixtures thereof.
 10. The closure bar of claim 1, comprising one ormore materials selected from the group consisting of nickel, aluminum,titanium, copper, iron, cobalt, and alloys thereof.
 11. The closure barof claim 1, wherein each center void region is configured to be sealedby a method selected from the group consisting of: brazing, welding,sealing with an interference-fitted plug, and sealing with a threadedfitting.
 12. The closure bar of claim 1, wherein: the center void regiondefines an interior surface; and the interior surface is coated with amaterial that is configured to prevent the phase-changing material fromreacting with the first cold closure bars.
 13. A heat exchanger corecomprising: a bottom end sheet; a plurality of alternately stackedindividual hot and cold layers, the cold layers defining a hot layerinlet region and a hot layer outlet region; and a top end sheet;wherein: each individual hot layer includes: a hot fin element forming aplurality of parallel open-ended hot channels adapted to pass a fluidtherethrough; a parting sheet separating each individual hot layer fromthe adjacent individual cold layer; and two hot closure bars positionedon opposite sides of the fin element, parallel to the open-ended hotchannels and extending the length of the open-ended hot channels; eachindividual cold layer includes: a cold fin element forming a pluralityof parallel open-ended cold channels adapted to pass a fluidtherethrough; a parting sheet separating each individual cold layer fromthe adjacent individual hot layer; a first cold closure bar, positionedon a first side of the cold fin element proximate the hot layer inletregion, parallel to the open-ended cold channels and extending thelength of the open-ended cold channels; and a second cold closure bar,positioned on a second side of the cold fin element proximate to the hotlayer outlet region and opposite the first cold closure bar, parallel tothe open-ended cold channels and extending the length of the open-endedcold channels; wherein the second cold closure bar is the closure bar ofclaim
 1. 14. The heat exchanger core of claim 13, wherein: eachindividual hot layer comprises two hot closure bars, each defining a hotclosure height between 0.64-25 mm (0.025-1 inch); and each individualcold layer comprises two cold closure bars, each defining a cold closureheight between 0.64-25 mm (0.025-1 inch).
 15. The heat exchanger core ofclaim 13, wherein the heat exchanger core is manufactured by one or moreprocesses selected from the group consisting of: additive manufacturing,hybrid additive manufacturing, subtractive manufacturing, and hybridadditive subtractive manufacturing.
 16. A method of producing a closurebar adapted for use in a heat exchanger core, the method comprising:forming a closure bar, the closure bar defining a center void region;partially filling the center void region with a phase-changing material;and sealing the closure bar, thereby containing the phase-changingmaterial within the center void region.
 17. The method of claim 16,wherein: the center void region is configured to be sealed by a methodselected from the group consisting of: brazing, welding, sealing with aninterference-fitted plug, and sealing with a threaded fitting; and theclosure bar comprises one or more materials selected from the groupconsisting of nickel, aluminum, titanium, copper, iron, cobalt, andalloys thereof.
 18. The method of claim 16, wherein: the closure bar isconfigured to be subjected to a flow of a hot fluid having a hot fluidoperating temperature; the phase-changing material has at least onephase-changing point that is between an initial temperature and the hotfluid operating temperature; wherein the at least one phase-changingpoint is selected from the group consisting of: melting and boiling; thephase-changing material is configured to: change phase in a forwarddirection as the flow of hot fluid over the closure bar begins, therebyslowing a rate of temperature increase by absorbing a latent heat as thephase-changing material changes phase in the forward direction; andchange phase in a reverse direction as the flow of hot fluid over theclosure bar ceases, thereby slowing a rate of temperature decrease byliberating the latent heat as the phase-changing material changes phasein the reverse direction; wherein the forward-reverse directions areselected from the group consisting of: boiling-condensing andmelting-solidifying.
 19. A method of operating a heat exchanger core toreduce a rate of change of temperature in at least one portion thereof,wherein the heat exchanger core includes a closure bar having a centervoid region partially filled with a phase-changing material and sealed,the phase-changing material has at least one phase-changing point thatis between an initial temperature and a hot fluid operating temperature,and the closure bar is disposed in a region of the heat exchanger corethat is configured to receive a hot fluid having a hot fluid operatingtemperature, the method comprising: initiating a flow of the hot fluidto the heat exchanger core; slowing a rate of temperature increase byabsorbing a latent heat as the phase-changing material changes phase ina forward direction; ceasing the flow of the hot fluid to the heatexchanger core; and slowing a rate of temperature decrease by liberatinga latent heat as the phase-changing material changes phase in a reversedirection; wherein: the phase-changing material has at least onephase-changing point that is between an initial temperature and the hotfluid operating temperature; wherein the at least one phase-changingpoint is selected from the group consisting of: melting and boiling; thephase-changing material is configured to: change phase in the forwarddirection as the flow of hot fluid over the closure bar begins, therebyslowing a rate of temperature increase by absorbing a latent heat as thephase-changing material changes phase in the forward direction; andchange phase in the reverse direction as the flow of hot fluid over theclosure bar ceases, thereby slowing a rate of temperature decrease byliberating the latent heat as the phase-changing material changes phasein the reverse direction; and the forward-reverse directions areselected from the group consisting of: boiling-condensing andmelting-solidifying.
 20. The method of claim 19, wherein: the centervoid region is configured to be sealed by a method selected from thegroup consisting of: brazing, welding, sealing with aninterference-fitted plug, and sealing with a threaded fitting; and theclosure bar comprises one or more materials selected from the groupconsisting of nickel, aluminum, titanium, copper, iron, cobalt, andalloys thereof.